This invention relates to laryngeal mask airway devices (LMA-devices). Such devices are useful in facilitating lung ventilation in unconscious patients by forming a low pressure seal around the patient's laryngeal inlet, avoiding the known harmful effects of the endotracheal tube, which forms a seal within the windpipe (trachea).
LMA-devices of the types disclosed in UK Patent Nos. 2111394 and 2205499 have become accepted items of equipment for rapidly and reliably establishing an unobstructed airway in a patient in emergency situations and in the administration of anaesthetic gases, and have found use in most countries of the world. A disadvantage associated with the use of such a mask is encountered in a patient who is at risk from vomiting or regurgitating stomach contents while unconscious since although the device forms a seal around the laryngeal inlet sufficient to permit artificial ventilation of the lungs, the seal is sometimes insufficient to prevent lung contamination during retching, vomiting or regurgitation.
A partial solution to this problem is disclosed in U.S. Pat. No. 4,995,388 in which reliance is made upon a combination of an improved peripheral continuity of seal pressure against the laryngeal inlet and the provision of a drainage tube to conduct gastric contents away from the laryngeal inlet. However, one embodiment of such a system is itself disadvantaged by the fact that the removal of such gastric discharges can be achieved only after the seal between the LMA device and the laryngeal inlet/oesophagus has been breached. Another embodiment provides for removal of gastric drainage without breaching the seal between the LMA device and laryngeal inlet/oesophagus, but this proved awkward to insert and caused throat irritation.
A more successful solution to this problem has been provided by the gastro-laryngeal mask airway device disclosed in U.S. Pat. No. 5,241,956 and European Patent 651664. In that device, a drainage tube passes through the posterior aspect of the mask and through the distal end of the inflatable cuff of the mask to open in alignment with the patient's oesophagus. However, the drainage tube must be sufficiently rigid at its distal end to withstand the pressure within the inflated cuff and it has been found that this may make proper insertion of the deflated device into the patient's throat more difficult than either necessary or desirable.
In a modified gastro-laryngeal mask airway device disclosed in International Patent Application WO 97/12680, provision is made for the distal half of the mask to be of softly compliant construction, and to ensure against collapse of the drainage tube when the cuff is inflated. Also, the mask has a flexible leading edge for facilitating correct insertion into the throat of the patient.
European Patent Application 796631 and U.S. Pat. No. 5,632,271 disclose an LMA device which further facilitates insertion into the throat of the patient, an LMA device includes a drainage tube, which opens into the distal tip of the mask, passes along the posterior aspect of the flexible airway tube and emerges from the mouth of the patient just below the upper incisor teeth. For practical purposes this device works well but has the following limitations.
A disadvantage of this back-to-back tube orientation is that it confers a degree of instability to the mask when the device is in place, permitting the possibility of loss of seal between the mask and laryngeal inlet. Another disadvantage of the back-to-back tube configuration is that it confers to the tubular elements of the device an undesirable degree of stiffness so that movements of the head and neck of the patient occasioned, for example, by surgical manipulation or positioning, may result in undue harmful pressure being exerted on the surrounding tissues of the upper airway passages.
Another disadvantage is that the inserting index finger tends to slip off the airway and drainage tube due to lack of purchase. A still further disadvantage is that the inserting index finger may be damaged by the teeth of the patient because of the greater combined diameter of the back-to-back tubes.